1. Field of the Invention
The present invention relates to a process for controlling a braking-force distribution in a vehicle. Front and rear wheel braking-force distribution is controlled by regulating a braking liquid pressure ratio for front and rear wheel brakes, based on a difference between front and rear wheel speeds.
2. Description of the Related Art
Techniques for controlling a front and rear wheel braking-force distribution to eliminate the difference between the front and rear wheels, and to achieve an ideal braking-force distribution are conventionally known, from Japanese Patent Publication No.51-26584, Japanese Patent Application Laid-open No.6-144178 and the like.
In such known techniques, optimal braking forces, corresponding to loads applied to front and rear wheels, are provided by conducting the control of the front and rear wheel braking-force distribution to eliminate the difference between the front and rear wheel speeds. This is based on the following principle: when a braking force B is generated for a tire receiving a vertical drag force N from a road surface, a slip rate .lambda. of the tire is represented, simplistically, in a very small region by the following equation: EQU .lambda.=K.times.(B/N)
(wherein K is a constant)
The ideal braking-force distribution is to ensure that the front and rear wheel braking forces are proportional to the vertical drag force. Therefore, the front and rear wheel slip rates .lambda. may be equalized. Thus, if the vehicle speed is represented by V.sub.V, and the wheel speed is represented by V.sub.W, the slip rate .lambda. is determined according to the following equation: EQU .lambda.=(V.sub.V -V.sub.W)/V.sub.V
Therefore, if the braking-force distribution is controlled so that the front and rear wheel speeds V.sub.W are equal to each other, the front and rear wheel slip rates .lambda. can be equalized. More specifically, control is conducted so that the rear wheel speed V.sub.W is equal to the front wheel speed V.sub.W by controlling the braking liquid pressure for the rear wheels.
In the known techniques, however, the behavior of the entire vehicle is not taken into consideration, and depending upon the operational state of the vehicle, there is a room for improvement in an aspect of steerage stability performance, especially, during braking when the vehicle is abruptly turning.